Add via parameter on join room requests as per MSC4156 #4

Job	Run time
Unit tests	4m 7s
Build for Windows (windows, amd64)	2m 8s
Linting	5m 11s
Build for Linux (linux, amd64)	3m 56s
Build for Linux (linux, 386)	1m 37s
WASM build test	0s
Initial tests passed	1s
Sytest (${{ matrix.label }})	0s
Upgrade tests	0s
Complement (${{ matrix.label }})	0s
Integration tests	0s
Upgrade tests from HEAD-2	0s
Integration tests passed	2s
Update Docker images	0s
	17m 2s

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